Why do we use mat board? Can't we just pop an image into a frame without it?
Well, yes you can, but there are a few good reasons not to. Firstly, a mat keeps the image away from the glass. Why is that important? A mat creates an air gap between the artwork and the glass which prevents the image from sticking to it in time. How can you get around that without using a mat? You can try a spacer, a little plastic strip that sits between the image and the glass. That way you can frame an image without using a mat.
Now, a mat does have other functions too. The width of the mat can define the look of a framed piece. In my opinion I would not use a mat smaller than 2 and a half inches. However, I love playing with mat sizes... A small image can look really great with a large mat! have a play around, personal taste counts.
In this image the focal point is the photo - not the frame or the mat. Being a larger mat than normal draws your eye into the image.
A few more things mat board....
For a portrait I like using a skin tone, as it sets off the skin colour of the person of interest in the picture.
A mat can bring out the focal point in an image, which can also be done with a double or triple mat. Pick the colour that's the main focal point of the image and use it as the double or triple, with a plain colour as the outer colour. That way you can enhance the colour of the main image without using a bright colour for the whole mat. The image below used a triple mat, with the middle mat picking out the colour in the picture.